1. Field of the Invention
The invention relates to permeable membrane gas separation systems. More particularly, it relates to the prevention of condensation in such systems.
2. Description of the Prior Art
Permeable membranes capable of selectively permeating one component of a gas mixture are considered in the art as a convenient, potentially highly advantageous means for accomplishing desirable gas separations. To realize this potential in practical commercial operations, membrane systems must be capable of achieving and maintaining a desired degree of process efficiency, without undue maintenance or an unacceptable decrease in membrane life because of environmental factors associated with their use.
One such factor relates to the condensation of the constituents of the feed gas on the surface of the membrane. Such condensation can lead to lower permeation rates, corrosion, increased maintenance and decreased membrane life. In addition, condensation in membrane systems can result, in some instances, in a contamination of desired product streams. Because of such condensation, therefore, more membrane surface area is commonly required for a given gas separation operation. As a result, both capital costs and maintenance costs are increased over those that would be incurred for membrane systems free of condensation problems.
It is important, therefore, that efforts be made in the art to minimize or eliminate condensation in membrane systems. One approach that has been employed for this purpose is to superheat the feed to the membrane system and to individually insulate the membrane modules included in a membrane system in order to maintain the superheat conditions therein. The superheat is typically supplied from external sources, such as steam or electrical heaters. Another approach involves predrying the feed stream by means of an adsorbent or a refrigerant dryer to a temperature dew point that is lower than the membrane operating temperature.
While such approaches serve to minimize or eliminate condensation, it will be appreciated that the capital and operating costs associated therewith are relatively high. Preheaters thus typically require an external energy source, and the insulation for individual membrane assemblies is relatively expensive and can make access to the membrane for maintenance purposes troublesome. Dryer systems likewise tend to be expensive, both in terms of operating costs and capital expense.
While solutions to the problem of condensation in membrane systems have thus been developed, a need remains for further improvement in the art, such development to enable condensation to be minimized or eliminated at reduced initial capital cost and lower operating and maintenance costs than are obtainable in the prior art practices. Such improvement in the art would contribute to the technical and economic feasibility of the use of permeable membrane systems in a wide variety of commercially significant gas separation operations.
It is an object of the invention, therefore, to provide an improved membrane separation system and process in which the problem of condensation is obviated.
It is another object of the invention to provide a membrane separation system and process containing improved means for eliminating or minimizing condensation of feed gas constituents on membrane surfaces.
With these and other objects in mind, the invention is hereinafter described in detail, the novel features thereof being particularly pointed out in the appended claims.